One-pipe hydraulic shock absorbers, widely used in the automotive and other industries, operate under relatively high hydraulic pressures, on average about 20 bars, with peaks of as high as 100 bars. To cope with such high operating pressures, sealing of the pressurized oil opposing the shock absorber piston—sealing which takes place between the shock absorber rod and the rod guide seat normally formed through a bush fitted in fluidtight manner inside the shock absorber body—is performed by a sealing assembly of the type shown in FIG. 1, which comprises at least three members: a conical rubber pad A fitted to a bush T and having a sealing lip, which pad constitutes the actual sealing member sliding, in use, on the shock absorber rod; a lock washer B on bush T, this latter being inserted in fluidtight manner inside a body S defined by a one-wall pipe; and a contrasting member C interposed between rubber pad A and washer B. Normally, bush T is also provided with a guiding liner R providing the sliding seat for the rod.
Known sealing assemblies of the type shown in FIG. 1 are however not completely satisfactory, by being relatively bulky and relatively complicated to assemble on account of the number of connected parts involved, and by having worsening performances with temperature decreasing. The rubber pad A, in particular, is currently made of a special fluorocarbon synthetic elastomer known as FKM, which has a minimum operating temperature of minus 15° C., whereas current applications call for a minimum operating temperature of minus 40° C.
EP1074760B1 describes a shock absorber rod sealing assembly specially designed to withstand fatigue stress and so operate effectively for a relatively long period of time. The sealing assembly described in EP1074760B1, however, is only suitable for so-called two-pipe shock absorbers designed to operate at relatively low pressures, on average 5 to 15 bars, and in which fall-off in performance at very low temperatures is less of a problem.